A method for fabricating a monocrystalline silicon layer over a non-crystalline mask layer such as silicon dioxide is disclosed in co-pending and commonly assigned U.S. Patent application Ser. No. 608,544, which is a continuation of Ser. No. 338,958, METHOD FOR GROWING MONOCRYSTALLINE SILICON THROUGH A MASK LAYER, J. F. Corboy, Jr. et al. filed Jan. 12, 1982 and in Ser. No. 553,305, METHOD FOR GROWING MONOCRYSTALLINE SILICON ON A MASK LAYER, J. F. Corboy, Jr. et al. filed Nov. 18, 1983. In the fabrication technique disclosed therein, a semiconductor substrate having a monocrystalline portion at a surface thereof is provided. A mask layer of a material such as silicon dioxide is formed over the substrate surface and an aperture corresponding to a monocrystalline portion of the substrate is generated in the mask layer. Silicon is then epitaxially deposited in a two stage process which is now referred to as epitaxial lateral overgrowth (ELO).
In the first stage of the ELO process silicon is deposited from a gas mixture which comprises a silicon-source gas. This forms monocrystalline silicon on exposed monocrystalline silicon surfaces although it also forms non-monocrystalline silicon on the mask layer. In the second stage both the deposited monocrystalline silicon and any non-monocrystalline silicon formed on the mask layer are exposed to a silicon-etching gas so as to remove the non-monocrystalline silicon from the mask layer while retaining a portion of the deposited monocrystalline silicon. When this deposition and etching cycle is repeated an appropriate number of times a monocrystalline silicon layer is ultimately formed on the mask layer. Following the formation of a monocrystalline silicon layer on the mask layer, cavities can be formed by etching the monocrystalline silicon in areas corresponding to the mask apertures. This will create a plurality of electrically isolated monocrystalline silicon islands which might be effectively utilized in silicon-on-insulator (SOI) device applications.
In commonly assigned U.S. Pat. No. 4,482,422, METHOD FOR GROWING A LOW DEFECT MONOCRYSTALLINE LAYER ON A MASK, J. T. McGinn et al. issued Nov. 13, 1984, the quality of the deposited moncrystalline silicon is disclosed to be strongly dependent upon the configuration and orientation of the mask aperture(s). This reference teaches that when performing ELO from a substrate surface which is parallel to a {100}-type plane the edges of the mask apertures should be parallel to one of the &lt;010&gt;-type directions lying in that plane. It is also disclosed that to produce high quality crystalline material the aperture shape should be rectangular with a length/width aspect ratio as high as other design and processing constraints will permit.
Although methods for forming high quality monocrystalline silicon formed by ELO have been disclosed, a problem nonetheless exists with respect to the inclusion of a void in a portion of the monocrystalline layer. As described in U.S. Pat. No. 4,482,422, a void is formed in the monocrystalline layer adjacent to the mask substantially midway between neighboring mask apertures. This void, which is inherent in the previously described processing, can pose a significant problem when forming SOI islands having relatively thin monocrystalline silicon layers. In an effort to overcome this problem, the present invention was discovered.